In the normal function of speech production, mastication and swallowing, the functioning tissues of the oral cavity consist of mobile and nonmobile structures. Mobile structural elements include the tongue, cheeks, lips and the soft palate, whereas the nonmobile elements are the hard palate, mandible and teeth. The structures interact in specific combinations to produce speech, swallowing and mastication. For example, to initiate and execute a swallow, the teeth are brought together, lips are closed, intraoral pressure is built up, the anterior portion of the tongue presses against the anterior portion of the hard palate, and the tongue dorsum rolls posteriorly over the palate, which forces saliva or a food bolus into the pharynx. For speech articulation, precise contacts are needed whereby consonantal sounds are produced by touching the palate with the tongue in very specific accurate contact areas, and vowels by permitting varying air streams to flow. For mastication of food, all of the oral musculature are brought into play, viz.: the tongue, lips and cheeks aid in carrying the food bolus to the teeth, a food table, and in preventing the food from dispersing during trituration.
The tongue, being the major articulator of the oral structures, must adjust for each speech sound. The tip, the edges and the base thereof must move some times as fast as thirty times per second, and each movement must hit the target, hard palate and teeth, at which it is aimed, with extraordinary accuracy. If it misses by even a fraction of an inch, the wrong sound will be produced.
A mature speaker relies heavily for this performance on touch, sense of cutaneous pressure, and kinesthesis, awareness of position and movement of the speech mechanism. The reliance includes more than sensations of touch and kinesthesis, it includes the neural process by which one perceives his body in relation to objects and space. It is this perceptual system by which we are literally in touch with our environment. The "feel" of speech is thus vital for normal performance, and plays a role in the speech transmitter system.
The speech transmitter system has at least two roles. It has an afferent role in transmitting the code of nerve impulses generated by the speech receptors to central parts of the speech system. The system also has an efferent role in transmitting patterns of motor impulses from the central speech system to the peripherial speech effector system. The tactile-kinesthetic transmitter system is utilized in speech control and monitoring function. If these speech receptors are not receiving and converting stimulation into codes of nerve impulses, there is dysfunction of the transmission system and reduced significant impulses of the central speech regions. As a result, there occurs a reduction in transmission of the motor impulses that have been organized in higher centers. Thus, decreased sensory input leads to decreased motor output which results in inaccurate production of speech. Equally, sensory and motor controls are involved in the feeding and swallowing mechanisms.
An abnormal oral environment may show impairment due to abnormality of the nonmobile and or mobile elements. Whereas the palate, mandible or teeth are nonmobile, they may be amenable to correction or reconstruction by surgical and or prosthetic intervention, such as is not within the purview of the present invention. Abnormalities of the mobile features of the oral environment may be the result of structural deficiency, such as a cleft palate, other congenital anomaly or cancer surgery of the tongue as an acquired defect. Functional impairment also may be congenital, developmental or acquired. Development of abnormal muscle patterns leading to oral and facial imbalances is present in "tongue thrusting". Acquired neurological functional abnormalities are due to stroke and head injuries. When there are disturbances of the neurogenic motor controls for speech, individuals will experience difficulty with strength, range of motion and or coordination of movements of the tongue, lips and soft palate, resulting in unintelligible speech and or swallowing. Individuals experiencing these difficulties are named "dysarthric", their speech may sound slurred, dysrythmic or hypernasal.
Current speech pathology intervention, that is speech therapy, aims at improving strength, range of motion and coordination of speech musculature. One known method of improving the strength of contact, the range of motion and the accuracy of the tongue and lips is called the "resisted movement" technique. For example, if the individual has difficulty in raising the anterior part of the tongue, the clinician applies graded pressure in a downward direction to the tongue while requesting the individual to attempt to lift his tongue against this resistance. The procedure may succeed in increasing or triggering additional muscular activity and the tongue tip may show increased movement upwards. Three or four maneuvers by the clinician should precede each request for the patient to raise the tongue without the presence of the downward pressure. The device generally available and used is a tongue depressor. Such training requires individual sessions between patient and speech therapist. One objective of such tongue exercises is to improve the strength, range of motion and accuracy of the tongue-palate contacts for speech and swallowing. The available capacity must be directed into specific neuromuscular patterns to achieve different maximal accuracy. This is accomplished by helping the patient through a process of "successive approximations" until accurate tongue-palate contacts are made.
A second possible approach is the placement of a prosthesis which provides palatal augmentation to compensate for tongue movement dysfunction. These prostheses must be designed individually to fit the patient and the use of such prostheses is limited by several factors: First, the patient's teeth must be suitable to support a prosthesis properly; a maxillofacial prosthodontist is needed to design, produce and fit the device; and finally, the cost must be considered.